The present invention relates to triaryl substituted imidazoles which antagonize the metabolic effect of glucagon. This invention also relates to compositions containing such compounds and methods of treatment using such compounds.
Diabetes is a disease process derived from multiple causative factors and characterized by elevated levels of plasma glucose. Uncontrolled hyperglycemia is associated with an increased risk for microvascular and macrovascular diseases, including nephropathy, retinopathy, hypertension, stroke and heart disease. Control of glucose homeostasis is, therefore, a major approach to the treatment of diabetes.
Glucagon is a major counter regulatory hormone that attenuates the inhibition of liver gluconeogenesis by insulin. Glucagon receptors are found primarily in the liver, although their presence has been documented in kidney, pancreas, adipose tissues, heart, smooth muscles of vascular tissues, and some regions of the brain, stomach and adrenal glands.
Type II diabetics have elevated levels of plasma glucagon and increased rates of hepatic glucose production. The rate of hepatic glucose production positively correlates with fasting blood glucose levels in type II diabetics. Therefore, antagonists of glucagon are useful in improving insulin responsiveness in the liver, decreasing the rate of gluconeogenesis and lowering the rate of hepatic glucose output resulting in a decrease in the levels of plasma glucose.
A monoclonal antibody to glucagon (Glu-mAb) has been utilized to test the acute effects of attenuation of glucagon action in streptozotocin-treated diabetic rats (Brand et al., Diabetologia 37:985, 1994). In contrast to a control antibody, injection of Glu-mAb attenuated the postprandial increase in blood glucose in moderately hyperglycemic rats (ie., rats with a moderate impairment in insulin secretion). In severely hyperglycemic rats (ie., rats with severely impaired insulin secretion), Glu-mAb injection did not lower blood glucose levels, but potentiated the hypoglycemic effect of a suboptimal dose of insulin. These data suggest that attenuation of the action of glucagon in these models leads to increased sensitivity to the action of insulin, but does not lead to decreased blood glucose levels in the absence of insulin. On the other hand, a monoclonal antibody to glucagon was effective in lowering plasma glucose levels in diabetic rabbits independent of insulin effects (Brand et al., Diabetes, 45:1076 (1996). While these data support the notion that antagonism of glucagon action will provide beneficial therapy for both type I and type II diabetics, this hypothesis could be more rigorously tested if a specific non-peptidyl glucagon antagonist were available.
The regulation of glucagon homeostasis is also mediated by the hormone insulin, produced in the .beta. cells of the pancreas. Deterioration of these cells is typically observed in Type I diabetics, and abnormalities in the function of these cells may occur in patients presenting the symptoms of Type II diabetes. Thus, a glucagon antagonist might have utility in treating Type I diabetics.
The glucagon receptor is expressed in kidney tissues where glucagon has been demonstrated to have an effect on electrolyte homeostasis including the ions sodium, potassium, chloride, magnesium, calcium, and phosphate and the non-electrolytes urea and water (Ahloulay et al., Am. J. Physiol., 269: F225, 1995). A glucagon antagonist may have use in treating disorders involving electrolyte imbalance. The kidney is also gluconeogenic in response to glucagon (Amores et al., Molec. Cell. Biochem., 137: 117, 1994) and an antagonist would act to lower glucose production in kidney furthering the treatment of diabetes.
Glucagon receptors are present in the heart and in smooth muscles. Glucagon has a direct effect on cardiac output and heart rate (Glick et al., Circ. Res., 22: 789 (1968); Farah, Pharm. Rev., 35: 181, 1983). A strong correlation has been observed in patients with hypertension and elevated plasma glucagon levels resulting from impaired hepatic catabolism (Silva et al., Heptatology, 11: 668, 1990). Antagonism of the effects of elevated glucagon levels may have an effect on certain types of hypertension, thus a glucagon antagonist may have utility in the treatment of certain types of hypertension associated with elevated glucagon production.
The primary role for glucagon and glucagon receptors associated with adipose tissues is to induce lipolysis, thus providing free fatty acids as a substrate for fat burning tissues (Saggerson et al., Biochem. J., 238: 387, 1986). An antagonist to this effect might be useful in treating conditions where there is excessive lipolysis of fat stores resulting from elevated glucagon levels, such as wasting disease (cachexia).
Glucagon and glucagon receptors have been localized to the hippocampus region of the brain (Hoosein and Gurd, Proc. Natl. Acad. Sci. USA, 81: 4368, 1984). This discovery suggests that glucagon may have a neuroendocrine role in initiating or elaborating basic behavior or somatic motor programs. Since glucagon secretion is increased in response to low blood glucose levels, increased glucagon levels in the brain may initiate behavior to respond to low glucose levels, such as eating. Thus, chronic hyperglucagonemia may also result in a constant craving for food resulting in obesity. A glucagon antagonist may have utility in treating obesity by altering feeding behavior associated with a response to glucagon.
The compounds in the present invention are glucagon antagonists. The compounds block the action of glucagon at its receptors and thereby decrease the levels of plasma glucose. The instant compounds thus are useful as antidiabetic agents. Glucagon may have other direct effects on cardiac output, lipolysis, and feeding behavior and therefore may be useful as antihypertensive, anti-cachexia or antiobesity agents.